Tensioner for a chain, a belt or the like

ABSTRACT

A tensioner is provided with a female screw member for the tension adjustment of a belt or a chain screwed with a male screw provided a rotation force by a spring and a bearing in which the female screw member is inserted and constrains the rotation of the female screw member. 
     In this tensioner, an outer form of the female screw member is formed so as to correspond to a bearing hole of the bearing. By this, an approximately whole length of the female screw member is able to slide through the bearing hole, and the stroke length of the female member can be secured sufficiently even if the size of the device in a tension controlling direction is shortened.

BACKGROUND OF THE INVENTION

This invention relates to a tensioner which provides a fixed tension toa chain or a timing belt which drives a cam shaft of an engine in a carfor tensioning it.

Generally, a tensioner is used for an engine as a chain tensioner or abelt tensioner. When the slackness of the chain or the belt occurs bythe elongation or the abrasion thereof, the tensioner acts so as to pushit in a fixed direction directly or indirectly and to maintain a fixedtension.

FIG. 19 presents a conventional example of such tensioner. Asillustrated in FIG. 19, a male screw member 2 and a female scew member 3are inserted within a casing 1 being threaded each other. The male screwmember 2 is screwed with the female screw member 3 at the fore halfportion of the male screw member 2, while at the latter half portion ofthe male screw portion 2 a coil spring 4 is inserted through the outsidethereof. One end 4a of the coil spring 4 is inserted into a long groove1a formed within the casing 4 and another end 4b is inserted into a slitof the male screw member 2, whereby the male screw member 2 is providedwith a rotative force. On the other hand, the female screw member 3penetrates through a bearing 5 secured to an opening end (left end) ofthe casing 1, the top end thereof (left end) being covered with a cap 6.A hole of the bearing 5 wherein the female screw member 3 penetratestherethrough, is formed to be a non-circular shape such as a small ovalform or the like wherein opposite surfaces are deleted parallel and theouter form of the female screw member 3 is also formed to be a same one.In such a construction, the rotation of the female screw member 3 isrestrained by the bearing 5 and the rotative force from the male screwmember 2 changes to a pushing force to the female screw member 3,whereby the female screw member 3 advances directly in a drawing outdirection from the casing 1 (left direction). Accordingly, the cap 6 atthe top end of the female screw member 3 always urges the belt or thechain, whereby a constant tension is adapted to be maintained. In FIG.8, the numeral 7 is a boot capable of elongation or shrinkage whichcovers the opening end of the casing 1, and the numeral 8 is a seal boltscewed with a base end (right side) of the casing 1. These boot 7 andseal bolt 8 are provided in order to prevent the invasion of dusts frominside and outside of the engine into the casing 1 and to prevent theleakage of lubricant oil in casing 1 to the outward.

However, in such construction, it is necessary to be provided with thefore half portion wherein the male screw portion 2 is screwed with thefemale screw member 3 and the latter half portion wherein the coilspring is inserted through the outside thereof. In this case, a size ofthe male screw member determines a dimension of the device. As a result,a whole device becomes long in an axial direction. This direction is onewhich controls the tension of the chain or the belt. Accordingly, inview of installing the engine at a very narrow space, a short size isdesirable and a long size is a fatal problem from the point ofinstallation.

In order to intend shortening of such size, such an idea is proposed inwhich the male screw member, the female screw member, and the coilspring are combined with so as to be piled up in a diameter direction(Utility Model Laid-Open No. 62(1987)-115554. In this device, the femalescrew member screwed with the male screw member is rotated by the aid ofthe coil spring, whereby the male screw member is adapted to advancethrough the screwed portion. Since thus the male screw member is adaptedto advance, a portion of the male member where performs a straightadvancement being supported by a bearing is formed to be a non-circularsectional area agrees with the bearing, thereby constraining therotation of the male screw member itself. This male screw member ispossible to advance until a screw portion (circular sectional area)formed at the male screw member abuts against the bearing. However, insuch a construction, the stroke of the advancing male screw member isstopped by the screw portion having a circular sectional area.Therefore, the stroke of the male screw member can not be securedsufficiently and the length for the tension controlling of the chain orthe belt becomes smaller even if the shortening of the whole device ispossible. By this, an adjustable range thereof is reduced and thepracticability is also decreased.

In the conventional technic, when the device is long, the installationthereof to the engine or the like is difficult. On the other hand whenthe device is shortened, its stroke becomes short, whereby the range ofthe tension control is reduced.

The object of this invention is to provide a tensioner such as a chain,a belt or the like.

The object of this invention is to provide a chain, a belt or the likewhich satisfies the miniaturization of the device and the security of asufficient range of the tension control.

SUMMARY OF THE INVENTION

This invention is provided with a female screw member threaded with amale screw member rotated with a spring and a bearing which constrainsthe rotation of the female screw member by the inserion of the femalescrew member, an outer form of said female screw member being formed soas to correspond to the bearing hole. By this, an approximately wholelength of the female screw member is possible to slide through thebearing hole, whereby the length of the stroke of the female screwmember can be sufficiently secured even if the size of the device in thetension controlling direction is shortened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, FIG. 2 and FIG. 3 are a sectional view, a left side view, and aright side view in an embodiment of this invention resectively. FIG.4(a), (b) and (c) are a sectional view, a left side view and a rightside view of the female screw member respectively. FIG. 5 is a partiallybroken side view of the casing. FIG. 6(a) and (b) are a front view and aside view of the bearing member respectively. FIG. 7(a)-(d) are sideviews in various modifications of the female screw member. FIG. 8(a) and(b) are respectively a side view and an enlarged sectional view ofanother example of this invention. FIG. 9(a) and (b) are respectively asectional view and an elevation view of a supporting member of the aboveanother example. FIG. 10 to 12 are a stopper member of the above anotherexample wherein (a) is a sectional view, (b) is a plan or a side viewrespectively. FIG. 13, (a) and (b) are respectively a plan view and aside view of a bearing in the above another example. FIG. 14(a) and (b)are a plan view and a side view of a spacer in the above example. FIG.15 and FIG. 16 are respectively a perspetive view of the materialportion and a sectional area of the material portion thereof whichexplane the attached conditions of the bearing and the spacer in theabove another example. FIG. 17 is a sectional view in a further anotherexample of this invention. FIG. 18 shows a modification of thesupporting member, wherein (a) is a central sectional view, (b) is aplan view and (c) is a side view thereof. FIG. 19 is a partly brokenside in the conventional device.

DETAILED DESCRIPTION OF THE INVENTION

The embodiment of this invention is hereinafter described with referenceto the accompanying drawings.

FIG. 1 is a sectional view of an example of this invention applied to abelt tensioner. FIG. 2 and FIG. 3 are respectively a left side view anda right side view thereof. A hollow portion 12 in the axial direction isformed to a casing 11 wherein an attaching hole 11a to an engine or thelike is formed at the outside thereof, said hollow portion 12 beingincorporated with male screw member 20, female screw member 30 and coilspring 40 therein. An axial portion 21 at the top end side (left endside) of the male screw member 20 is screwed with the female screwmember therein, while a fixed portion 22 of a base portion (right side)thereof is inserted into a dent portion 16 formed at the base portion ofthe hollow portion 12 together with a washer 15, thereby being supportedrotatively. In this case, a screw portion 23 is provided through thewhole outer circumference of the axial portion 21 of the male screwmember 20. On the other hand, in the female screw member 30, a screwportion 31 screwed with the male screw portion 23 is formed at a part ofthe inner circumference. Further, a bearing member 50 is provided at thetop end portion (left end portion) of the casing 11. As illustrated inFIG. 6, the bearing member 50 is formed to be a approximately trianglestar shape as a whole and the bearing hole 51 is opened at the centralportion thereof. Further, outwardly extending portions from the bearinghole 51 toward three directions are bent at approximately right angle toform engaging pieces 52. This engaging piece 52 is inserted withinengaging groove 13 formed at the top end portion of the casing 11,thereby fixing the bearing member 50 to the casing 11. For this purpose,the engaging groove 13 in which the engaging piece 52 is inserted isformed at the top end of the casing 11 as shown in FIG. 5. The engaingpiece 52 is not only formed to bend at approximately right angles asdescribed above,but also may be projectingly formed outwards in the sameplane as the forming plane of the bearing hole 51. In this case, it isdesirable to thicken the thickness of the bearing member 50 in order todecrease the surface pressure against the casing 11. Further, theforming number of the engaging piece 52 are not defined to three asshown in FIG. 6, but can be designed to be arbitrary. If the numbersincrease, the torque of the spring 40 can be bindly adjusted. Although,for instance, when the three engaging pieces 52 are provided (FIG. 6),the mim, adjustment angle thereof becomes 60°. Accordingly, a fineadjustment is possible. Further, u type groove 13 described above canbe, of course, provided in casing 11 according to the number of theengaging piece 52. The bearing hole 51 in this example is bored to beapproximately an oval form consists of a set of parallel lines and twoarc lines which connect opposite end portions of the parallel linesrespectively. The female screw member 30 is inserted into the bearinghole 51, to slide in a constrained status of the rotation. For thispurpose, the outer form of the female screw member 30 is formed to beone corresponds to the bearing hole 51 by cutting an axial portion 33 tobe parallel as shown in FIG. 4. Since approximately a whole body of thefemale screw member 30 is possible to be inserted into the bearing hole51, the stroke length of the female screw member 30 can be securedsufficiently.

A stopper flange 32 having a large diameter is formed at the baseportion of the female screw member 30. The advancement of the femalemember 30 is stopped by the abut of the stopper flange against thebearing member 50, whereby drawing out of the female screw member can beprevented.

The coil portion of the coil spring 40 is inserted through the outwardof the female screw member 30, one end thereof 41 being bent in theaxial direction of the casing 11 to insert into a long groove 14 formedin the hollow portion 12 of the casing. On the other hand, another end42 of the coil spring 40 is inserted into a slit 24 formed at the fixedportion 22 of the male screw member 20. By this, the male screw member20 is allowed to rotate by the coil spring 40, thereby the female screwmember 30 is adapted to drive to go straight on. In such a constructionwherein the male screw member 20 is inserted into the female screwmember 30 and the female member 30 is inserted into the coil spring 40,the miniaturization of the device can be attained by shortening thelength in the axial direction of the device, or the length in thetension controlling direction. Further, according to this example, thefemale screw member 30 is only threaded with the male screw member 20coaxially. Accordingly, there exists no supporting port at the bottom ofthe hollow portion 12 in the casing 11, thereby being able to designshorter the length in the axial direction thereof so much.

Furthermore, in this example a cylindrical collar 70 is inserted betweenthe female screw member 30 and the coil portion of the coil spring 40.Although the collar 70 is not always necessary because this has norelation to the substantial performance as a tensioner, the installaionof this collar prevents the contact and the invasion of the coil portionto the female screw member 30 due to the bending of the coil portion,whereby the slide of the female screw member 30 becomes to be moresmooth. The base portion of such coller 70 is inserted into a stepportion 25 formed at the outer circumference of the fixed portion 22 inthe male screw member 22, thereby carrying the supporting thereof.

Further, in this example a cap member 71 is inserted at the top endportion of the female screw member 30, the top end portion of this capmember 71 being adapted to abut against the belt. The numeral 72 is aspring pin forcibly inserted into thefemale screw member 30 and the capmember 71 in order to prevent the drawing out of the cap member 71. InFIG. 1, the numeral 60 is a snap ring engaged with the top end surfaceof the casing 11, which prevents the slipping out of the bearing member50. The numeral 61 is a cover which coats the top end of the casing 11and the numeral 62 is a boot wherein the base portion thereof is adheredto the cover 61, the top end portion of the casing 11 being coated bythese. The numeral 63 is a garter spring which prevents the slipping outof the boot 62. Further, a seal bolt 67 is screwed with a base side ofthe casing 11 by way of a seal plate 64 and a washer 65, whereby thebase side is adapted to be sealed. Furthermore, the numeral 68 is astopper pin inserted into the casing 11 from outside so as to be able toinsert or draw out, the top end thereof being adaptd to attain withinthe slit 24 of the male screw member 20. For this purpose, a dentportion llc wherein the seal member 18 consists of an elastic memberwhere the stopper pin 68 is insertable therethrough is inserted, isformed and further a penetrated hole 17 of the stopper pin 68 whichinterconnects the dent portion 16 of the fixed portion 22 of the malescrew member 20 is provided. By this, the rotation of the male screwmember 20 is locked in a state where the stopper pin 68 is insertedtherein. Since this example is used in air as a belt tensioner, alubricant oil is sealed in the interior of the device. In order toperform a smooth flowing of the lubricant, oil holes 69 are formed infemale screw member 30, bearing member 50 and collar 70 properly. Thisoiling hole 69 is not only formed as a penetrated hole, but also abroken portion formed at the end surface of the collar 70 may be used.Further, in this example an air escaping hole 73 which communicatesoutward is formed at the cap member 71, thereby being able to correspondto internal volume changes of the boot 62 and the casing 11. In thisexample, the cap member 71 is used as an upper portion so that thelubricant oil may not leak from the air escaping hole 73.

The air escaping hole 73 is not only provided to the cap member 71, butalso the penetrated hole 17 of the stopper pin can be used as an airescaping hole. In other words, the penetrated hole 17 can be used as anair escaping hole by romoving the stopper pin and further removing theseal member 18 inserted into the dent portion 11c. In this case, thewhole device is used turning it sideways so that the penetrated hole 17may be upwards in order to prevent the leakage of the lubricant oil fromthe penetrated hole 17.

The construction of this invention described above engages the collar 70on the male screw member 20 threaded with the female screw member 30thereon, inserts this within the coil spring 40, latches another endportion 42 of this coil spring 40 to the slit 24 of the male screwmember 20, installs the cap member 71 at the top end of the female screwmember 30 and inserts the bearing member 50 at the axial portion of thefemale screw member 30, thereby forming a subassembly. Then, thissubassembly is inserted within the casing 11 and further a fixed portion22 of the male screw member 20 is inserted into the casing 11 togetherwith washer 15 so as to be releasably supported, said subassembly beingprevented from going out of place by the aid of a snap ring 60. The snapring 60 is engaged with a groove llb formed at the top end of the casing11. After securing the cover 60 having a fixed one end of the boot 62 tothe top end of the casing 11 due to caulking or adhesion, another end ofthe boot 62 is secured to the cap member 71 with garter spring 63,thereby sealing the top end portion of the casing 11. After that, a toolsuch as driver or the like is inserted into the slit 24 of the malescrew member 20 from the base side of the casing 11, whereby the malescrew member 20 is allowed to rotate to wind up the coil spring 40 sothat the energy may be stored therein. In this state, the stopper pin 68is inserted to perform a rotation locking. Further, after the lubricantoil is injected into the casing 11, the sealing is carried out by theseal bolt 67. By this, the construction of the device is completed. Whenthis device is fixed to the engine or the like and the stopper pin 68 isdrawn out, the male screw member 20 rotates by the aid of the coilspring 40, whereby the female screw member 30 goes ahead to urge thebelt.

FIG. 7 shows various kinds of modefication of the outer form in thefemale screw member 30. In the example of FIG. 7 (a), though the axialportion 33 of the female screw member 30 is circular form, a partthereof is broken like a straight line. In FIG. 7(b) broken areas areformed at 4 places at equivalent intervals and the outer form of theaxial portion 33 is formed to be approximately a regular square havingarc line at each four corner area.

In FIG. 7(c), broken areas are formed at 3 places and the outer form ofthe axial portion 33 is formed to be approximately a triangle. In FIG.7(d), the broken area of the arc line is formed at 3 places. Even inthese modifications, the outer form of the axial portion 33 insertedinto the bearing hole of the bearing member is a non-circular form. Theaxial portion 33 of the female screw member 30 may be formed to besquare outer form.

Accordingly, the rotation of the female screw member 30 is constrainedby forming the bearing hole of the bearing member so as to correspond tothe form of this member, thereby being able to perform the straightadvancement.

Since the above example is applied to the belt tensioner, the lubricantoil is sealed in the interior of the casing. However, when this isapplied to an engine of an autobicycle as a chain tensioner, there is noneed of the above lubricant oil because it is secured in the engine oilin a soaking state. In this case, since there is no need of boot, thelength of the female screw member 30 can be more shortened. By this, thelength of the device in the controlling direction can be shortened.

FIG. 8(a) and (b) represent other embodiments of this invention.

In this embodiment, the same elements as in the embodiments describedabove are shown by the same numbers and deleted the explanationsthereof.

This embodiment is different from the embodiment described above in thepoints that the fixed portion 22 of the male screw member 20 is changedto washer 15 to support it by a cylindrical supporting member 80 havinga bottom without being provided with collar 70, the cap member 71 isclosely constructed without being provided with air escaping hole 73,the construction between cover 61 and casing 11 is sealingly constructedusing a seal ring 81, a stopper member 82 is used in place of stopperpin 68, and the spacer 83 intervenes between the bearing member 50 andthe casing 11. However, this embodiment is the same as the embodimentdescribed above in the terms of that the construction thereof is atripple one wherein the male screw member 20 is insrted into the femalescrew member 30 and the female screw member is inserted into the coilspring 40.

The supporting member 80 is, as shown in FIG. 9(a) and (b), formed to bea cylindrical shape having a bottom using a stiff material through thewhole body theseof. In other words, the cylindrical portion 80b isdisposed in upright from the bottom portion 80a. An outer diameter ofthe cylindrical portion 80b is formed to a size insertable into a dentportion 16 formed at the base portion of the cavity portion 12 of thecasing and the inner diameter of the cylindrical portion 80b is formedto a size in which the fixed portion 22 of the male screw member 20 isinserted rotatively. Further, an escaping hole 80c used for assemblingof the tensioner and winding of the spring 40, is provided at thecentral portion of the bottom 80a. Such supporting member 80 is insertedinto the dent portion 16 of the casing and the fixed portion 22 of themale screw member 20 is inserted into the cylindrical portion 80b. Insuch a construction, the supporting member 80 lies between the dentportion 16 of the casing 11 and the fixed portion 22 of the male screwmember 20 to prevent a direct contact of the male screw member to thecasing 11, thereby being able to prevent the wear of the casing 11caused by the rotation of the male screw member 20. By this, since thecasing 11 can be formed by a light material such as aluminium, its alloyor a synthetic resin, it is possible to decrease the weight of thecasing. Further, since the cylindrical portion 80b of the suportingmember 80 extends to cover the outer surface of the fixed portion 22 ofthe male screw member 20 and the supporting force increases, the morestable support of the rotation can be performed. Furthermore, since thesupporting member 80 is an independent part, the mechanical workingthereof is easy as compared with the working of the casing 11 itself andthe precision working also becomes easy because of its simpleconstruction. Accordingly, this has a merit which is possible to performeasily the working suitable to a stable rotation of the male screwmember 20.

This supporting member 80 may be, as shown in FIG. 18,(a), (b), (c),provided with projections 80d at the outer circumpherence of thecylindrical portion 80b. The projection 80d is is formed so as to beelongated in a longitudinal direction and tapered downward from an upperend brim of the cylindrical portion 80b to downward (in a bottom 80adirection) along the outer side of the cylindrical portion 80b. By this,when the supporting member 80 is forcibly inserted into the dent portion16 of the casing, the projection 80d cuts into the inner circumferentialwall of the dent portion 16, whereby the rotation of the supportingmember 80 is securely obstructed. Since the above projection 80d is thusformed in order to obstruct the rotation of the supporting member 80, atleast only one formation of the project may be sufficient.

The cover 61 of this embodiment is attached sealingly to the casing 11with a seal ring 81 attached in a circumferential groove 85 provided atthe outer surface of the casing 11 as shown in FIG. 8(b). The seal ring81 consists of an elastic body and when the cover 61 is attached to thecasing 11 in a state where the seal ring is inserted in thecircumferential groove 85, the seal ring 81 adheres to the inner surfaceof the cover 61 and the outer surface of the casing 11, thereby sealingtherebetween. By this, the invasion of dusts from outside and theleakage of the lubricant oil sealed in the interior of the casing 11 areprevented. In a construction wherein such seal ring 81 is used, the airtight between the cover 61 and the casing 11 can be securely carriedout. Accordingly, there is no need of a high accuracy of the sige forthe prevention of the air tight at the attached portion of the cover 61.This causes the easiness of the working and the improvement of theproductivity.

The stopper member 82 of this embodiment is, as shown in FIG. 8(a) and(b), formed by bending a spring plate member 6 coated with a syntheticresin a around the all outer circumstance in symmetry with respect tothe left and the right, abutting a pressing portion 82a against the topportion of the cap member 71, and latching two pertions 82b, 82b formedoppositely at the opening ends to a forming position of the attachinghole lla, the casing 11. The above synthetic resin a slide preventiveperformance which prevents the slipping off of the pressing portion 82aof the stopper member 82 from the top portion of the cap member 71. Thisis due to the fact although the top and of the cap memeber 71 whichcontacts with an urged member (not shown) is formed an arc-like or asphere for maintaining a good contact with it ever if the contact pointthereof slips off with a stroke of the female member 30, when the flatsurface of the stopper member 82 abuts the top end of the cap member 71having such surface, it is apt to be drawn out by slip and a goodstopper performance can not be obtained.

FIG. 10 to FIG. 12 represent modifications of the slide preventive meansof the stopper member 82.

The stopper member 82 shown in FIG. 10 and FIG. 11 consist of springplate a and a hole 82c and an arc-like dent 82d projects to outward arerespectively provided at the approximately central portion of thepressing portion 82a. Into this hole 82c and the dent 82d is inserted apart of the top portion of the cap member 71 and latched with it. Bythis latching, the slide prevention is performed each other and thestopper member 82 is prevented from coming off. The stopper member 82 inFIG. 12 is partly coated with a synthetic resin 82e having a slidepreventive performance at near the abutting position of the cap member71 of the pressing member 82a and the latching portion 82b.

This stopper 82 can be removed by widening the opening end portion torelease the latching state of the latching portions 82b,82b. The stoppermember 82 is easily attached to the casing 11 and is able to lock theadvancement of the female screw member 30 in a stable state.Accordingly, there is no occurrence that the use of the stopper becomesimpossible by unprepared advancement of the female screw member at thetime of conveyance and storage.

Further, in this embodiment the spacer 90 consists of the stiff materialintervenes between the bearing member 50 and the casing 11. The bearingmember 50 used at this time is provided the bearing hole 51 at thecentral area thereof and the engaging pieces 55 project outward at 90 ofintervals at the outside portions respectively as shown in FIG. 13. Thespacer 90 is, as shown in FIG. 14, provided an interconnecting hole 91which communicates with the bearing hole 51 of the bearing member 50 atthe central area thereof, said interconnecting hole 91 being formdapproximately a ring shape. At the outside portions of the spacer 90,receiving pieces 92 having type are formed at 90 of intervals. As shownin attaching states in FIG. 15 and FIG. 16, the spacer 90 is insertedbetween the top end surface of the casing 11 and the bearing member 50.In this insertion, the receiving piece 92 is adapted to be inserted intothe u type groove 13 of the casing 11 first. In this state, theattaching piece 55 of the bearing member 50 to which a rotation force ofthe male screw member 20 acts is adapted to avoid the direct contactwith casing 11 by being wrapped with the receiving piece 92 of thespacer 90. In other words, even if the rotation force of the male screwmember transmitted through the female screw member 30 acts on theattaching piece 55 of the bearing member 50, the attaching piece 55 doesnot contact with casing 11 directly and the urged pressure thereof isreceived by the receiving piece 91 of the spacer 90. By this, since therotation force from the attaching piece 55 does not act on the casing 11directly, the wear at the contact portion of the attaching piece 55decreaes. As a result, there is no need of making the case 11 with ahard material having anti-wearing property. Accordingly, it is possibleto endure for use sufficiently even if making it with aluminium or itsalloy, synthetic resin, or other light material. Therefore, this hasmerits in the points that the weight of the casing 11 can be decreasedand the selection of the material is also enlarged.

Further, in FIG. 15, the numeral 95 is a groove wherein a snap ring 60for prevention of coming off of the bearing 50 is inserted therein.

FIG. 17 shows another embodiment of this invention.

This embodiment is a modified example of the cover 61 and the boot 62 inFIG. 8 which use a cover member 100 formed integrally with a sameelement.

Namely, in FIG. 17, the cover member 100 consists of a cylindrical coverportion 101 and a boot portion 102 continuously connected with the covermember 101. These are elastic member of rubber and formed intergrally.At the inner surface of the cover portion 101 and the boot portion 102,a ring-like projections 101a, 101a and 102a are formed respectively. Thecasing 11 are connected with the cap member 71 by the aid of that theprojection 101a, 101a and 102a are inserted respectively into thecircumference grooves formed at the outer surface of the casing 11 andthe cap member 71, and further the connecting portion is securedsealingly by the elastisity of the elastic member.

Such cover member 100 is easy in preparing as compared with oneconnected after the cover and the boot are separately constructed.

Further, the sealing of the base side of the casing 11 in the above eachexample may be used with a sealing cork consists of an elastic membersuch rubber and the like in place of the seal bolt 67. In this case, thescrew portion at the casing side 11 is not provided, but a step portionwhich latches with a large diameter of ring like rib provided at thesealing cork may be only provided, whereby the working thereof becomesmore easy .

In this invention as described above, since the outer form of the femalescrew member which performs tension control of a belt, chain or the likecan be formed to correspond to the form of the bearing hole whichconstrains the rotation thereof, almost whole length of the female screwmember slides through the bearing hole, thereby being able to maintainthe stroke length thereof sufficiently. Accordingly, the length of thedevice in the axial direction can be shortened without sacrifice of thestroke length of the male screw member, whereby the miniaturization ofthe device can be obtained.

What we claim is:
 1. In a tensioner for a chain, a belt or the likewhich comprises a male screw member and a female screw member installedwithin a casing in a screwed state, a spring which provides a rotationforce to said male member and a bearing into which the female screwmember is inserted so that the female screw may advance in a axialdirection by the rotation of the male screw member together withconstraining the rotation of said female member;said tensioner beingcharaterized in that said female screw member is screwed with said malescrew member at the outside thereof and said spring is provided at theoutside of the same female screw member thereby forming a tripleconstruction.
 2. A tensioner for a chain, a belt or the like accordingto claim 1 wherein a cylindrical collar is provided between said femalescrew member and said spring.
 3. A tensioner for a chain, a belt or thelike according to claim 1 wherein said bearing is provided with anengaging piece inserted into said casing to constrain the rotation ofsaid bearing.
 4. A tensioner for a chain, a belt or the like accordingto claim 1 wherein the outer form of said female screw member is anon-circular form.
 5. A tensioner for a chain, a belt or the likeaccording to claim 1 wherein a supporting member which supports the malescrew member rotatively is provided between the male screw member andthe casing.
 6. A tensioner for a chain, a belt or the like according toclaim 5 wherein an escaping hole is formed in a cap member provided atthe top end of the female screw member, said cap member being used as anupper portion of the casing.
 7. A tensioner for a chain, a belt or thelike according to claim 5 wherein a penetrated hole for a stopper pin,which locks the rotation of the male screw member when engaged with saidmale screw member, is provided in the casing, said penetrated hole beingprovided at an upper portion of the casing so as to be able to be usedas an escaping hole.
 8. A tensioner for a chain, a belt or the likeaccording to claim 1 wherein a portion between the female screw memberand the casing is coated with boot and the end portion of the boot isconnected to a cap attached to the casing, thereby being allowed tointervene a seal ring between the cap and the casing.
 9. A tensioner fora chain, a belt or the like according to claim 1 wherein a slidepreventive means which prevents the sliding against the top end portionof the female member in the stopper is provided at the abutment portionthereof.
 10. A tensioner for a chain, a belt or the like according toclaim 1 wherein a lubricant oil is sealed in the casing and oil holesfor smooth lubrication of said lubricant oil are formed in said femalescrew member, in said bearing member and in a collar, respectively. 11.A tensioner for a chain, a belt or the like according to claim 1 whereina stopper which locks the advancement of the female screw member by theabutment of the top end portion of the female screw member is removablyattached to the casing.
 12. A tension for a chain, a belt or the likeaccording to claim 11 wherein a slide preventive means which preventssliding against the top end portion of the female screw member in thestopper is provided at the abutment portion thereof.
 13. A tensioner fora chain, a belt or the like according to claim 1 wherein a supportingmember supports the male screw member rotatively between said male screwmember and the casing.
 14. A tensioner for a chain a belt or the likeaccording to claim 1 wherein an attaching portion of the bearing whichconstrains the rotation against the rotation force of the male screwmember is formed to the bearing so as to latch to the casing and thespacer intervenes between the attaching portion where the rotation forceacts thereto and the casing.